At least 24 people died when cyclone Pam hit Vanuatu at the weekend, authorities have confirmed. The storm flattened buildings, wrecked infrastructure and has left more than 3,000 people in the South Pacific island nation displaced.

As the full scale of the storm remained unclear due to the archipelago’s remote nature and its severely damaged telephone network, a statement from the national disaster management office raised the death toll from single digits and said that 3,300 people were sheltering at 37 evacuation centres.

It is feared that those numbers could rise still further as communications with outlying islands are restored. Initial indications are that the devastation to rural communities is far more significant than even in the capital city, Port Vila, which is itself very badly damaged.

As the first rescue teams to reach those islands warned of significant damage, the president of Vanuatu, Baldwin Lonsdale, warned that climate change was contributing to more extreme weather conditions.

Speaking at a UN conference in Sendai, Japan, on Monday, said 90% of buildings in Port Vila had been damaged or destroyed by the category five storm, which saw winds of up to 250km/h (150mph).

“It’s a setback for the government and for the people of Vanuatu,” he said. “After all the development that has taken place, all this development has been wiped out.”

Lonsdale said the cyclone seasons that the nation had experienced were directly linked to climate change.

“We see the level of sea rise … The cyclone seasons, the warm, the rain, all this is affected ,” he said. “This year we have more than in any year … Yes, climate change is contributing to this.

“I am very emotional … Everyone has that same feeling. We don’t know what happened to our families … We cannot reach our families; we do not know if our families are safe. As the leader of the nation, my heart hurts for the people of the whole nation.”

Anote Tong, the president of Kiribati, also at the conference, urged action: “It is time to act … Let us match the rhetoric of these international gatherings with pledges and commitments as leaders to do our best to improve conditions and lives of those who need it most.”

The aid agency Care International said it had just received its first update from another of the nation’s 83 islands, Tanna, to the south of Port Vila, which was even more directly in the path of the storm.

Tom Perry from the organisation said he had talked to a colleague newly arrived on Tanna: “The basic information he gave us was that the damage in Tanna is significantly worse than in Port Vila. There’s an immediate need for water there.”

There was no news as yet on deaths, but the situation looked very bad, Perry warned. “Most people in outer islands live completely rural lives,” he said. “They grow what they eat, and this will have wiped out their entire food stocks. People live in very simple accommodation, huts made of timber and palm leaves. There’s no way buildings like that are going to withstand a category five cyclone.

“We’re gravely concerned about it, there’s no question. There is a sense that if we don’t get a response quickly, people are going to be running out of water and food.”

Getting aid to more remote communities would prove very hard, he said: “If you look at the logistics involved in an operation like this, it’s incredibly difficult.

“You’ve got a country of 83 islands spread over hundreds and hundreds of kilometres. Getting around Vanuatu is difficult in a normal situation, let alone when you have no communications, you don’t know the status of the airstrips, boats aren’t really travelling yet.”

Even in Port Vila, where clearing-up work was beginning, many people had yet to hear word from loved ones elsewhere.

A local resident kneels near debris on a street near damaged homes in Port Vila. Photograph: Reuters

Perry said: “People are very resilient here. This is quite a poor place, and people are very tough. But there’s also shock. Most people still don’t have contact with their loved ones. There’s a significant population in Port-Vila who are from somewhere else in the country, and people just aren’t able to get in contact with their family. There’s a real concern about that.”

Unicef has expressed serious concerns over children who have been displaced or affected by the cyclone. The organisation estimates that at least 60,000 children may be at risk, and have called for funding to provide child health needs, food and water.

Communications in the Port Vila province of the island have now been “almost fully restored”, according to telecommunications provider Digicel, allowing information to flow more freely to and from disaster areas.

Several countries have also pledged additional aid and funding for the stricken island nation. The Australian foreign affairs minister, Julie Bishop, pledged $5m in support, and New Zealand has offered $2.5m.

Bishop said on Monday that Australia was working closely to provide support, and had sent several military planes with supplies and aid workers.

“We are aware that this has been a most devastating cyclone,” she said. “The impact will be felt for quite some time ... We stand ready to assist in the long-term recovery efforts.”

Cyclone Pam has travelled south after passing over Vanuatu, and reached New Zealand on Monday. The cyclone was downgraded from a category five storm but conditions have been poor in some areas of the country.

In Gisborne, in north-east New Zealand, about 40 people were evacuated from sea-level homes, and schools were closed.

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The Guardian’s Joshua Robertson is attempting to uncover the full scale of the disaster wrought by cyclone Pam. We will be adding his tweets in here as he travels around the country talking to Ni-Vanuatus about the crisis. There will be radio silence from him at times when he goes out of range of satellites